Commensurate Growth of Densely Packed PTCDI Islands on the Rutile TiO₂(110) Surface

Abstract

We have studied the deposition of perylene-tetracarboxylic-diimide, PTCDI, on the rutile (1 × 1)-TiO2(110) surface. At variance with other polyaromatic hydrocarbons, like acenes, PTCDI displays a significant interaction with this dielectric substrate. At moderate substrate temperature (∼400 K), first layer molecules aggregate into two-dimensional islands corresponding to a (1 × 5) commensurate phase. According to our surface diffraction, STM, and NEXAFS studies, the substrate accommodates one PTCDI molecule per unit cell, atop each oxygen row. Because of steric repulsion, molecules lie on their long edge, tilted by ∼35° with respect to the surface. This constraint determines a strong π–π coupling between adjacent molecules, resulting into a geometry similar to that reported for acenes on (1 × 1)-TiO2(110), but quite uncommon for perylenes.